Water Purification Device

ABSTRACT

A device ( 1 ) for purification of water driven by gravity through a purification unit between an upper dirt water container ( 2 ) and a lower clean water tank ( 3 ). A backwash system may be integrated, the system comprising a receptacle ( 8 ) for accumulation of the backwash water to prevent consumption thereof by mistake.

This application is a continuation of application Ser. No. 14/064,413filed Oct. 28, 2013, which is a continuation-in-part of InternationalApplication PCT/DK2011/050132 with an international filing date of Apr.27, 2011, which are hereby incorporated by reference in their entiretyas if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates to water purification devices. Especially,it relates to water purification devices with a filtration membrane andan upstream dirt water container.

BACKGROUND OF THE INVENTION

Portable purification devices with serially arranged antimicrobialresins and air-tight membrane filters suffer from the fact that air maybe trapped between the resin and the membrane which blocks for a properflow of water through the system. For this reason, water purificationsystems have been developed with vent conduits that provide a passageinto atmosphere from the volume between the resin and the membrane.

An example is disclosed in U.S. Pat. No. 6,454,941 for a gravity filterwith a resin in a compartment above a membrane that formed as avertically oriented cellular honeycomb structure. An air vent conduitextends from the volume between the resin and the filter membrane up tothe upper edge of the resin below water inlet cap. Water in the devicecannot by mistake be driven all the way up to the air vent conduit exit,because a goose-neck conduit for water consumption has its water exitbelow the air vent conduit exit, and water would leave that conduitfirst.

Another example is published in U.S. Pat. No. 6,638,426 for a gravityfilter with a vent tube that is provided above a filter that hasvertically arranged, hollow membrane fibres. The vent tube extendscentrally through an upper resin chamber and ends higher than the topwater inlet above the resin. The vent tube extends from a lower,tangential fluid divider, which has a form of an inverted funnel. Thefluid divider has apertures for water to flow down from the resinthrough the apertures and into the housing with the filter.

These systems have dedicated means for venting the volume above themembranes. Other water purification systems are disclosed with venttubes extending through an upper dirt water container to above the waterlevel in the dirt water container. Examples are given in U.S. Pat. No.4,749,484, U.S. Pat. No. 4,978,449, U.S. Pat. No. 4,759,474, U.S. Pat.No. 4,800,018, and EP404573. Alternative systems with vent tubes outsidethe dirt water container are disclosed in GB1112072, U.S. Pat. No.3,709,362, EP245585, U.S. Pat. No. 5,281,309. Further vent systems aredisclosed in DE3828008, U.S. Pat. No. 3,281,108, U.S. Pat. No.6,159,363, U.S. Pat. No. 7,276,169. As it appears from thesedisclosures, portable systems have vent tubes extending through theupper dirt water container, whereas for stationary systems, vent tubesthat imply air escape from the upstream side of the filter medium canextend through the upper dirt water container or extend outside theupper dirt water container. Thus, there seems to be a systematiclimitation for portable devices in this respect, which is due to thedesired compactness of these devices, although it implies somelimitations for the possible design of the portable water filtrationdevices.

International patent application WO2008/110166 discloses in FIG. 7 agravity driven water filtration system with an upper dirt watercontainer connected by a tube to a filtration unit. In use, thefiltration unit oriented vertically, and air from the filtration unit isexiting in an upward direction through the tube and into the dirt watercontainer against the stream of dirt water from the container. Inpractice, this is no problem, although for start up, it is moreconvenient to open a forward flush valve in order to empty the devicefor air quickly.

If the filtration unit of the system disclosed in FIG. 7 ofWO2008/110166 would have a horizontal orientation, air would be trappedin the filtration unit, which is also the reason, why the module has avertical orientation when in use. However, even in a horizontalorientation, it would be possible to vent the system by opening aforward flush valve during feeding with dirt water from the oppositeend. Once air is flushed out of the system, this flush valve could beclosed again. An indication that the air is flushed out of the system isthe appearance of water at the exit from the flush valve. Thus, alsoduring proper operation in horizontal orientation, air trapping is noproblem for operation of this device, in principle.

Due to the relatively easy venting of the system of WO2008/110166 byusing the forward flush valve, such a horizontal orientation of thefiltration device may be tempting to use in other filtration systems, ifspace and compactness is a critical issue. Problem occurs however, ifsuch a system is not understood properly by the end user. For example,for the user not familiar with the system, the procedure for air ventingmay no be obvious, and the user may regard the system as not properfunctioning simply due to the fact that air trapped in the systemprevents a proper water flow from the clean water exit valve. Also, theforward flush valve may be mistaken as the clean water supply, and theuser may consume dangerously contaminated water coming from the dirtwater container without having passed the filter membrane. These risksmay appear hypothetical at first glance; however, it should be pointedout that such filter systems are used in emergency areas with sometimeshectic activity where a proper training of the user is not alwayspossible due to lack of resources or lack of time. In such situations,the risk for mistakes is high and may cause fatal results for the user

The above described system also suffers from the fact that no properclean water accumulator is provided, which implies a large risk forback-contamination, especially in emergency situations, wherecleaning-water is scarce, and the focus is not especially on hygiene.

A portable water purification system for emergency situations ispublished on the Internet onhttp://espwaterproducts.com/emergency-preparedness-water-disaster-relief.htm.The system comprises a top dirt water container covered by a prefilterfor removing debris and large sediment particles when water is added.The dirt water container contains an iodine tablet for destroyingbacteria and virus. Inside the dirt water container, a verticallyarranged sediment pre-filter is provided for removing contaminants downto 0.5 microns in size, including cysts. The lid of the clean water tankcontains a filter connector that is directly connecting the outlet ofthe sediment filter to the inlet of a vertically arranged multimediacartridge which removes industrial and agricultural contaminants as wellas chlorine, iodine, and bad tastes and odours. The multimedia cartridgeis provided below the lid and inside the clean water tank. The cleanwater tank is provided with a tap for dispensing of the purified water.

As the lid of the clean water tank is easily removable, contamination ofpurified water can easily become a problem if the lid is not properlyplaced, or it is removed in not sufficiently hygienic conditions. Thelatter is important when knowing that in emergency situations, but alsoin typical households in Africa's rural countryside, animals mix withhumans and may get easily access to the purification system and itssurroundings.

A further disadvantage of this system, as well as the systems disclosedin U.S. Pat. No. 6,454,941 and U.S. Pat. No. 6,638,426 is the fact thata continuous filling of water into the upstream tank leads to anoverflow in any downstream part. Thus, the user has to keep track of howmuch water is in the tank upstream of the filter relatively to how muchis in the downstream part in order not to waste water. The latter is animportant issue in emergency situations, where water is scarce.

For these reason, there is an ongoing effort to improve portable waterfiltration systems in the direction of higher safety anduser-friendliness, especially in connection with portable filters foruse in emergency situations.

DESCRIPTION Summary of the Invention

It is therefore the objective of the invention to provide improvementsin the art. Especially, it is the purpose to optimize user friendlinessand minimize the risk for accidents when using the device. Some of theimprovements are related to ease of transport and storage. Otherimprovements are related to prevention of air trapping in the filtrationunit without the necessity of interference by the user, even in caseswhere the filtration unit is oriented horizontally.

The device comprising a dirt water container for accumulating dirtwater, a clean water tank for accumulating purified water, and apurification unit, for example filtration unit, for purifying water fromthe dirt water container. The purification unit comprises a filterhousing enclosing a purifying medium separating an upstream side of thepurification unit from a downstream side of the purification unit, suchthat water inside the purification unit can flow from the upstream sideto the downstream side only through the purification medium, for exampleporous filtration membrane. The upstream side is connected to the dirtwater container for receiving dirt water into the upstream side and thedownstream side is connected to the clean water tank for dispensingfiltered water from the downstream side into the clean water tank.Optionally, the purification unit is arranged outside the clean watertank. The dirt water container is arranged above the purification unitfor driving water through the purification unit by gravity. The dirtwater container has a container outlet and the filter housing has anupstream inlet to the upstream side, wherein the container outlet andthe upstream inlet are fluid-flow-connected by a first flow connectorfor receiving dirt water from the dirt water container into the upstreamside of the purification unit. The device comprises a clean water tankfluid-flow connected to the downstream side through a downstream outletfor receiving filtered water from the downstream side. Optionally, theclean water tank is arranged below the purification unit.

Several options exist for the purifying medium, for example differentresins that release antimicrobials. Examples are resins that releasechlorine or iodine. Other options are granular activated carbon or othermedia that capture microbes and other particles. An example of suchother adsorptive medium is disclosed in U.S. Pat. No. 6,838,005 byTepper and Kaledin, where a fibrous matrix contains electropositiveadsorptive nano-particles. In this case, alumina nano-fibres areprovided in a porous glass fibre matrix filtering microbes by attachmentto the nano-fibres. The microbes and anorganic sediments are attractedby the highly electropositive charged alumina and stay permanently,unreleasable in the filter matrix. The purifying medium may also be acombination of several different media, for example halogen resins incombination with activated carbon.

Alternatively, the purification unit is a filtration unit, and thepurifying medium comprises a microporous filtration membrane. Onepreferred option is microporous hollow fibre membranes, for example abundle of hollow fibre membranes, although other types of microporousmembranes can be used as well. This can be combined with one or more ofthe other above-mentioned media, for example the fibrous matrix containselectropositive adsorptive nano-particles.

A water purification device according to the above has a usefulcombination of features. In addition, it is useful for forming the basisfor the following further improvements, especially for a portabledevice.

A Vent Tube

One independent improvement concerns easy venting of the upstream sideof the filtration unit, for which the following embodiment is useful. Inthis case, the upstream side of the filtration unit has an upstreamoutlet in the filter housing for outlet of fluid from the upstream side.A vent tube is connected to the upstream outlet; the vent tube extendsupwards, preferably outside the clean water tank, and has a vent openingfor venting air from the upstream side into atmosphere. Optionally, thevent tube extends upwards outside the clean water tank, although it canalso extend inside the dirt water tank.

The water from the dirt water container will be pressed by gravitythrough the upstream side of the filtration unit and from the upstreamside of the filtration unit into the vent tube. By this action, air willbe pressed into the vent tube by the water. Thus, if the vent opening isprovided higher than the bottom of the dirt water container, air in thevent tube will be pressed to a height corresponding to the water levelin the dirt water container. Thus, only in case of the water level inthe dirt water container being higher than the height at which the ventopening is arranged, a siphon effect will cause water to be forced outof the vent opening until the water level in the container has the sameheight than the height of the vent opening. In order not to lose waterunnecessary, the height of the vent opening advantageously is closer tothe top of the dirt water container than to the bottom of the dirt watercontainer. Especially, it should be approximately adjusted to themaximum water level in the dirt water container or higher. For example,the vent opening is provided at a reference height, the reference heightbeing at most 5 cm or 2 cm, or even only at most 1 cm, below an upperedge of the dirt water container, although it is also possible toprovide the vent hole above the upper edge of the dirt water container.

An option in case of the vent tube extending upwards outside the dirtwater container is to attach an upper part of the vent tube to an outerside of the dirt water container.

Backwashing

One independent improvement concerns safety for backwashing of thefiltration unit. Thus, in a further embodiment, the device comprises abackwash facility for the membrane filter in the filtration unit. Inthis case, the device comprises a manually compressible backwash bulbthat is fluid-flow connected, advantageously by a flexible hose, to thedownstream side for accumulation of clean water for backwash purposes.

Principles of such backwash facilities are generally known, for examplefrom the above mentioned international patent application WO2008/110166.The term “bulb” is used as a general term and comprises the specificembodiments of the bulb being a balloon or a bellow or other resilientlycompressible water chambers. A backwash tube is provided which is, forexample with a first end, connected to the upstream side for receivingcontaminated backflush water from the upstream side of the filtrationunit and, for example with an opposite end, connected to a backwashreceptacle for dispensing the into the backwash receptacle when water ispressed from the downstream side through the membrane to the upstreamside by compression of the backwash bulb and further from the upstreamside through the backwash tube into the backwash receptacle. Such areceptacle minimizes the risk for unintended consumption of contaminatedbackwash water.

Optionally, a lever is provided for compression of the backwash bulb forbackwash purposes by operating the lever, for example depression of thelever. In specific embodiments, the lever comprises a rigid lever tubefluid-flow connecting to the backwash bulb with the downstream outlet ofthe filter housing. In a further embodiment, the rigid lever tube has afirst end that is fluid flow connected to the downstream outlet, forexample mounted pivotal adjacent to the downstream outlet. The rigidlever tube has an opposite end, remote from the pivotal mounting at thedownstream outlet, the opposite and being provided with a handle foroperating the lever.

As a further option, the backwash receptacle is provided at a levellower than the filtration unit, which assures a proper flow into thebackwash receptacle. An even further option is provided if the backwashtube is connected to the backwash receptacle through a fluid entrance ofthe backwash receptacle, wherein the fluid entrance is surrounded bymultiple holes for preventing drinking therefrom; this improves usersafety.

In order for preventing backwash water to be pressed into the dirt watercontainer during backwash, in a further embodiment, a one way checkvalve is provided between the dirt water container and the upstream sideof the filtration unit.

Optionally, the above backwashing improvement is combined with the aboveindependent vent tube embodiment. In case of such a combination, thereis the possibility of a further improvement according to the followingembodiment, where the backwash tube is an integral part of the venttube. Thus, there is no need to provide a vent tube as well as aseparate backwash tube, but it is sufficient to provide a single tubewith a single tube interior that serves both purposes. Optionally, thecombined vent and backwash tube has a tube part downstream of the ventopening, which tube part is connected to the backwash receptacle.

Membranes Maintained in Water

A further independent improvement which, optionally, is combined withone or more of the above independent improvements, is presented in thefollowing. In this embodiment, the downstream side is connected to theclean water tank by a downstream outlet which is above the membraneswhen in proper use for filtration. This prevents emptying of thefiltration unit such that the membranes are maintained immersed inwater, which is important for polymer membranes, such as hollow fibremembranes, because a drying out can lead to collapse of the membranepores. For example, the downstream outlet is provided in the upper partof the filter housing. especially in the case, where the filtration unithas a horizontal orientation or an inclination from horizontal of up to45 degrees or up to 10 degrees, the downstream outlet is placed at aheight above the membrane in the filtration unit in order to maintain awater level above the membranes in the filtration unit.

A Distributor

A further independent improvement which, optionally, is combined withone or more of the above independent improvements, is presented in thefollowing. In this case, the improvement concerns a distributor fordistribution of water from the downstream side of the filtration unit.For transport of water from the downstream side of the filtration unitand into the clean water tank, the downstream side of the filtrationunit is connected to the clean water tank for flow of filtered waterfrom the downstream side in the filtration unit and into the clean watertank. In a further embodiment, this connection is achieved by adistributor. The distributor comprises an inlet channel for receivingfiltered water from the downstream side, a first distributor outlet fordispensing filtered water to the backwash bulb, and a second distributoroutlet for dispensing water into the clean water tank. Advantageously,the distributor also comprises a one-way check valve arranged betweenthe first distributor outlet and the second distributor outlet forpreventing backwash water from the compressible backwash bulb fromentering the clean water tank when water is forced backwards through thefirst distributor outlet due to compression of the backwash bulb. Forexample, the check valve is a ball valve. Such a valve can be providedin comprising a valve housing containing a ball and with a ball seat ina wall of the valve housing on a side adjacent to the fluid flowconnector and remote to the second filter housing outlet.

The distributor is advantageously but not necessarily combined with thebackwash lever as described above.

In a further embodiment, the distributor also comprises one-way ventvalve for venting air from the sealed clean water tank when water entersthe tank from the filtration unit. As the one way valve only allows airto leave the clean water tank when there is more than atmosphericpressure in the clean water tank due to filling of water in the tank,the valve is only open in combination with an outgoing air flow, whichprevents dust and microbes to enter the clean water tank. However, in afurther embodiment as an additional safety measure, the valve isprovided with an air permeable membrane that prevents microbes and dustto back enter the clean water tank. In this case, the valve may,optionally, be a two way valve such that air can enter the clean watertank, when water is dispensed from it through the tap, which furtherminimizes the risk for back contamination. In an even furtherembodiment, in order to prevent water escaping though the vent valve incase of overfilling of the clean water tank, the air permeable membraneis a hydrophobic membrane that prevents water to pass the vent valve.Alternatively, in order to prevent water escaping though the vent valvein case of overfilling of the clean water tank, the valve is providedwith a water stop, for example including a ball valve that closes thevalve when the clean water tank is filled.

Transportation

Further independent improvements which, optionally, are combined withone or more of the above independent improvements and variousembodiments above, are presented in the following. In this case, theimprovement concerns handling, storage and transportation. Theseembodiments are of general nature and useful not only for the embodimentwhere the purification unit is a filtration unit but for embodimentswith various types of purification media.

In order for the purification unit to be protected against damage whenhandling the device, the purification unit is advantageously arrangedinside the clean water tank or, alternatively, in a space between theclean water tank and the dirt water container, that is, above the cleanwater tank and below the dirt water container. The latter configurationgives access to the purification unit, for example in case ofreplacement, which can be advantageous relatively to the case, where thepurification unit is inside the sealed clean water tank.

Advantageously, this space is defined by an intermediate module havingcross sectional dimensions in the horizontal plane corresponding tocross sectional dimensions of the dirt water container and the cleanwater tank. For example, the dirt water container, the intermediatemodule, and the clean water tank form an integrated three-module systemin stacked conditions, where the intermediate module is supported by theclean water tank and, in turn, supports the dirt water container. Inorder to ease mount and demount of the purification unit, the firstfluid flow connector between the dirt water container and the upstreamside of the purification unit is a flexible hose.

Some embodiment, especially, good for storage and transport of thedevice comprise the following improvement. In these cases, the devicehas a connection between the clean water tank and the dirt watercontainer, the connection comprising means for varying the distancebetween the clean water tank and the dirt water container. Theconnection has a first state where the clean water tank and the dirtwater container are in a close position, which is a storage or transportstate, and the connection has a second state where the clean water tankand the dirt water container are in a remote condition, which is anoperational condition for water filtration. For example, the distancebetween the clean water tank and the dirt water container in the secondcondition is between 5 cm and 100 cm larger than in the close position.

Such means for varying the distance, optionally, comprises a set ofprofiles in sliding cooperation with the outer side of the clean watertank or the outer side of the dirt water container or both. For example,the clean water tank has grooves on its outer side which take up theprofiles in sliding cooperation. Alternatively, the dirt water containercould comprise such grooves.

In an alternative embodiment, the means for varying the distancecomprises a rotationally hinged profile with an angle varying relativelyto the clean water tank in dependency of the distance between the cleanwater tank and the dirt water container. For example, the profile ishinged in a first hinge at the clean water tank and is hinged in asecond hinge at the dirt water container. Optionally, in addition, thedirt water container has an upper opening which is dimensioned largerthan a cross section of the clean water tank in order to partly enclosethe clean water tank in storage condition. When this embodiment iscombined with the vent tube improvement above, the vent tubeadvantageously extends upwards inside the dirt water container in ordernot to get entangled with the other mechanical parts.

Various Embodiments

In the following, various embodiment are described that may be combinedwith the independent improvements above.

In order to provide sufficient gravity force for driving water throughthe membrane of the purification unit, in a further embodiment for thedevice, the dirt water container is arranged above the clean water tankat a distance from the clean water tank of at least 10 cm or at least 20cm, and, optionally, at most 40 cm or 30 cm. For example, the dirt watercontainer is arranged above the clean water tank and with a clearance ofat least 5 cm, or at least 10 cm or at least 20 cm between the cleanwater tank and the dirt water container. The distance is relativelyshort with a corresponding low pressure on the purification unit.

Especially in the case of the purification unit being a filtration unitwith a microporous filtration membrane, the low gravity pressure impliesan advantage, as particulate matter is kept relatively loose on theinfluent surface of the membrane, making backflush and cleaning easy andprolonging the lifetime of the membrane filter.

Due to the accumulating clean water tank, the flow through thepurification unit can be accepted to be rather low, because the devicecan filter water without interaction and surveillance by the user. Forexample, the dirt water container is filled in the evening, and thedevice may filter the water slowly during the night in order to providea tank full of water the next morning. Even in the case that the dirtwater container is filled despite the clean water tank not being empty,in which case there is more water in the dirt water container thanacceptable by the clean water tank, this is no problem, because theclean water tank is sealed and the water filtration will stop as soon asthe clean water tank is filled.

For example, the device is in the form of a portable device dimensionedto be easily carried by a single human. For example, the portable devicehas a dry weight of less than 30 kg. In addition, the volume of the dirtwater container is, optionally, less than 30 liters. As a furtheradditional option, the volume of the clean water tank is less than 30litres. However, the invention is not limited to be a portable deviceand the inventive features apply equally well to a larger facility, forexample as a clean water facility for a school, a hotel, or even acommunity.

The connections between the dirt water container and the purificationunit or the connection between the purification unit and the clean watertank may be rigid tubes, however, in order to facilitate assembling thedevice and for easing mount and demount of the purification unit, thefirst flow connector is advantageously a flexible hose, although this isnot strictly necessary. Optionally, the vent tube is also a flexibletube.

The clean water tank may be provided with an enclosure that can beopened for cleaning. In an alternative embodiment, in order to minimizethe risk for back contamination, the clean water tank has an enclosuresealed against the environment. The term “sealed against theenvironment” means that there are no holes in the enclosure, where dirtor microbes can enter the clean water tank directly from theenvironment. The term “sealed against the environment” is also valid inview of the tap that is provided with a drain valve for dispensing waterfrom the clean water tank through the tap, because, normally, the tap isclosed. In addition, an opening in the clean water tank is necessary forthe connection to the purification unit from which clean water isreceived; although, in principle, there is a connection from the cleanwater tank through the purification medium, for example membrane, of thepurification/filtration unit and through the connection to the dirtwater container and out into atmosphere, this connection can also beregarded as sealed, as no dust nor microbes can enter the clean watertank through the membrane. There may be provided further openings, likevent valves, that open to the atmosphere in the environment; however,this kind of opening only occurs in a controlled manner during outflowand possibly inflow of air when water is filled into the clean watertank or released from it. Such valves are also normally closed, thus,preventing entrance of dust and microbes, why also such valves are notin contradiction to the term “sealed against the environment” for theclean water tank. In addition, such valves may comprise an air permeablebut not water permeable microporous membrane preventing dust andmicrobes to pass such openings.

In order to safeguard that the clean water in the clean water tank isnot subject to contamination, the clean water tank may be provided withbiocidal means. An option is a biocide that is added to the water, forexample by a dispenser or by dissolution of a solid agent containing thebiocide. Alternatively, or in addition, the clean water tank maycomprise a biocidal agent on and/or in the walls of the clean watertank. For example, the inner wall may be provided with a biocide thatprevents proliferation of microbes on the inner walls of the clean watertank.

One example of providing the antimicrobial surface is by coating with anantimicrobial substance. A large number of different coatings areavailable. Examples of antimicrobial organosilane coatings are disclosedin U.S. Pat. No. 6,762,172, No. 6,632,805, No. 6,469,120, No. 6,120,587,No. 5,959,014, No. 5,954,869, No. 6,113,815, No. 6,712,121, No.6,528,472, and No. 4,282,366.

Another possibility is an antimicrobial coating that contains silver,for example in the form of colloidal silver. Colloidal silver comprisingsilver nanoparticles (1 nm to 100 nm) can be suspended in a matrix. Forexample, the silver colloids can be released from minerals such aszeolites, which have an open porous structure. Silver can also beembedded in a matrix such as a polymer surface film. Alternatively, itmay be embedded in the matrix of the entire polymer of the clean watertank wall during plastic forming processes, typically known as injectionmoulding, extrusion or blow moulding.

A silver containing ceramic, applicable for the invention, is disclosedin U.S. Pat. No. 6,924,325 by Qian. Silver for water treatment isdisclosed in U.S. Pat. No. 6,827,874 by Souter et al, No. 6,551,609 byKing, and it is known in general to use silver enhanced granular carbonfor water purification. Silver coating for water tanks is disclosed inEuropean patent application EP1647527.

Other antimicrobial metals that may be employed in connection with theinvention are copper and zinc, which, alternatively or in addition, maybe incorporated in an antimicrobial coating. An antimicrobial coatingcontaining silver and other metals is disclosed in U.S. Pat. No.4,906,466 by Edwards and references therein.

A coating may, in addition or alternatively, comprise titanium dioxide.Titanium dioxide can be applied as a thin film that is synthesized bysol-gel methods. As anatase TiO₂ is a photo catalyst, thin films withtitanium dioxide are useful on external surfaces that are exposed to UVand ambient light. Also, nanocrystals of titanium dioxide may beembedded within polymers. In addition, silver nanoparticles can becomplexed with titanium dioxide for enhanced effectiveness.

For example, a thin film coating may have a thickness as little as a fewmicrometer. A coating may in addition, or alternatively, comprise areactive silane quaternary ammonium compound, like it is known from thecompany AEGIS® under the trademark Microbe Shield™ used for airconditioning. When applied as a liquid to a material, the activeingredient in the AEGIS Antimicrobial forms a colourless, odourless,positively charged polymer coating, which chemically bonds & isvirtually irremovable from the treated surface.

Further options include quaternary ammonium coatings, for examplepolyethylene imine coatings with biocidal quaternary ammonium.

Some antimicrobial substances are able to migrate through polymermatrices. This implies that the coating may contain antimicrobialsubstances that are continuously renewed due to the migration from theinside of the coating to the surface of the coating. Therefore, in afurther embodiment, the material of the wall of the clean water tank ismade of a material containing an antimicrobial substance. Thisantimicrobial substance has the property to migrate from the inside ofthe material to the surface of the material.

Depending of the technology of coating, an inner wall biocidal surfacecoating can also be achieved by dipping into a bath. Processes likespraying may be applied of the respective dedicated surface or surfaces.

An additional option that may be incorporated in the clean water tank isan ultra violet (UV) lamp, for example as it is disclosed in US patentapplication No. 2005/258108. Such a lamp may be used in addition to thebiocidal means.

Apart or as an alternative to dispensing antimicrobials in the cleanwater tank, the clean water tank may be provided with a reservoirreleasing nutrients and/or pharmaceuticals to the clean water in theclean water tank. For example, clean water from the purification unitflows into the reservoir and enriches the water by dissolving aslow-soluble matrix inside the reservoir. For example, the matrixcontains an agent that is liberated upon dissolution of the matrix. Apossibility is water soluble glass that can contain a releasable agenteither dissolved in the glass itself or in voids between sintered glassbeads.

An example of a membrane filter inside the filtration unit is a ceramicfilter or a semipermeable polymer filter for microfiltration orultrafiltration. For example, the filtration unit comprises a pluralityof hollow fibre microporous membranes, optionally with the hollow fibremembranes being arranged in parallel and potted at both ends in a resinor being bend and potted only in one end. An example is given ininternational patent applications WO2008/110166 and WO2008/110172.Optionally, the hollow fibre membranes have an outer side of themembranes towards the upstream side and the inner side of the membranestowards the downstream side; this is normally called an outside-in flowconfiguration. Alternatively, the hollow fibre membranes have theirinner side towards the upstream side and the outer side towards thedownstream side, this is normally called an inside-out flowconfiguration. The term “microporous” covers microfiltration porosity aswell as ultrafiltration porosity.

Advantageously, the membrane filter unit is configured for stoppingvirus, bacteria and parasites with a size of more than 0.2 microns. Forexample, hydrophilic membranes are used with a microbe separation layerwith a pore size of less than 0.2 microns. Optionally, the filtrationunit comprises a microporous membrane, for example a bundle of hollowmicroporous fibres, having a membrane surface area of between 0.05 and0.6 m², for example between 0.1 and 0.3 m².

As an additional safety measure, a further embodiment comprises anadditional filtration or otherwise purifying media downstream of themicroporous membrane. An example of this additional filtration mediumcomprises a fibrous matrix containing electropositive adsorptivenano-particles. An example of such filtration medium is disclosed inU.S. Pat. No. 6,838,005 by Tepper and Kaledin. In this case, aluminanano-fibres are provided in a porous glass fibre matrix filteringmicrobes by attachment to the nano-fibres. The microbes and anorganicsediments are attracted by the highly electropositive charged aluminaand stay permanently, un-releasable in the filter matrix. The lifetimeof the filter depends on the level of contaminants in the influent waterand the capacity of the filter. Further such matrices are described inWO2008 110167.

For example, a bundle of hollow fibre microfiltration membranes isfollowed with a fibrous matrix containing electropositive adsorptivenano-particles. Virus not held back by the microfiltration hollow fibremembranes would then be captures by the matrix. The advantage is ahigher flow rate as compared to hollow fibres with ultrafiltrationcapabilities. Also, the matrix would capture microbes and otherparticles in case that the membrane ruptures or the potting material forthe membrane loses its hermitical seal; in view of the matrix being suchkind of redundant safety means, a combination of a bundle of hollowfibre ultrafiltration membranes followed by a fibrous matrix containingelectropositive adsorptive nano-particles is also useful. Instead ofhollow fibre membranes, other microporous membranes can be used in afiltration unit as described. Combinations of microporous filters and afibrous matrix containing electropositive adsorptive nano-particles aredisclosed in WO2008/110166.

An advantageous material for the capillary membranes is a compositioncomprising PolyEtherSulfone (PES), PolyVinylPyrrolidone (PVP) andzirconium oxide (ZrO₂), for example as described in European patent EP241 995 or in WO2009/019592.

In a further embodiment, the purification unit, for example filtrationunit, has a filter housing that is elongate tubular with a longitudinalaxis and is oriented with the longitudinal axis within at most 45degrees or 25 degrees or 10 degrees from a horizontal plane. Forexample, the purification/filtration unit has a horizontal longitudinalaxis or an approximately horizontal axis.

Compactness of the purification unit for portable systems is achieved toa great degree, if the filter housing is a tubular filter housing withrelatively small dimensions, for example with cross sectional dimensionshaving a circumscribed circle with a diameter of 100 mm at most. Anotheruseful dimension of the purification unit is a length of less than 50cm, for example less than 30 cm.

As an option, the dirt water container may comprise an antimicrobialsource, for example a halogen source. A tablet containing releasablechlorine, for example by dissolution or evaporation from a chambercontaining such tablet, is one possible option, although also otherkinds of dispensers may be used. Non limiting alternatives are microdosing systems releasing fluidic biocides, for example iodine orchlorine. Other alternatives include resins capable of releasing halogenbiocides or biocides based on non-halogenic substances.

Number references in the claims are not intended to limit the scope ofthe claims.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail with reference to thedrawing, where

FIGS. 1A-1D are drawings of the device, where A) illustrates the devicein an overview drawing; B) illustrates tube connections; C) shows acut-away illustration; and D) a view with the dispenser tap;

FIG. 2 is an exploded view of the device;

FIGS. 3A-3C illustrate the distributor, where A) is a line drawing ofthe upper side, B) is a drawing of the lower side, and C) a crosssectional drawing;

FIGS. 4A-4D illustrate a telescopic embodiment in A) an overview imageand B) an exploded drawing, C) an illustration of the tubing, and D) across sectional drawing;

FIGS. 5A-5D illustrate an embodiment with dirt water container connectedrotatably relatively to the clean water tank, where A) is an assemblydrawing, B) is an exploded drawing, C) shows part of the tubing, and D)shows the device in a collapsed state;

FIG. 6 illustrates an embodiment slightly amended relatively to FIG. 5with a non-detachable backwash bulb;

FIGS. 7A-7B show an embodiment of a filtration device in A) a threedimensional drawing and B) a cut-away three dimensional drawing;

FIGS. 8A-8B show an alternative embodiment with a lever for compressingthe backwash bulb, where a) is an overview drawing, and b) showsinterior features;

FIG. 9 is a sectional drawing of the alternative embodiment;

FIG. 10 is a drawing of a filter housing with bent hollow fibre filters;

FIG. 11 is a sectional drawing illustrating the water flow and anantimicrobial source.

DETAILED DESCRIPTION Preferred Embodiment

FIG. 1A is a drawing illustrating a device 1 with a dirt water container2 for accumulating dirt water and a clean water tank 3 for accumulatingfiltered water. An intermediate module 4 is provided between the dirtwater container 2 and the clean water tank 3. This intermediate module 4defines the distance between the dirt water container 2 and the cleanwater tank 3 when in stacked conditions as illustrated. In addition, theintermediate module 4 houses a filtration unit 5, which is shown in FIG.1B, where the intermediate module 4 is removed for sake of illustration.The filtration unit 5 comprises a filter housing 5′ enclosing amicroporous membrane filter and is on the filter's upstream sidefluid-flow connected to the dirt water container 2 for receiving dirtwater and is on the filter's downstream side fluid-flow connected to theclean water tank 3 for dispensing filtered water into the clean watertank 2. As illustrated, the dirt water container 2 is arranged adistance above the filtration unit 5 for driving water through thefiltration unit 5 and into the clean water tank 3 by gravity. Typically,the intermediate module 4 has a height of between 0.1 and 0.4 m.

The clean water tank 3 also has on its outer side a first cavity 6 foraccommodating a compressible backflush bulb 7, which during normaloperation is filled with clean water and rests inside the cavity 6. Forbackwash, the backwash bulb 7 may be removed from the cavity 6 andmanually compressed, by which water is pressed backwards through themembrane in the filtration unit 5 in order to remove particulate matterand biofilm from the influent surface of the membrane on the upstreamside. The pressure generated in the upstream side by the backwash watercloses a check valve between the upstream side in the filtration unit 5and the dirt water container 2 such that the backwash water is notpressed back into the dirt water container 2. Instead, the backwashwater is guided from the upstream side by a tube arrangement (shown as12, 12A in FIG. 1B) into a back wash receptacle 8, which is accommodatedin a second cavity 9 in the outer side of the enclosure of the cleanwater tank 2.

In order to minimize the risk for a user placing a drinking cup in thebackwash cavity 9 and filling the drinking cup with backwash water forconsumption, the upper part of the backwash receptacle 8 and the housingof the clean water tank 3 may be equipped with an additional valve (notshown) that only opens when the backwash receptacle is properly placedin the backwash cavity 9.

As a further precautionary measure, the fluid entrance, reference 8A inFIG. 2 and in greater detail in FIG. 6, of the backwash receptacle 8 isprovided with multiple holes 8B around the fluid entrance, makingdrinking from it extremely difficult, which indicates for the user, thatthe backwash receptacle is not intended for containing water forconsumption.

FIG. 1B is a different drawing without the intermediate module in orderto illustrate the tubing. A flexible dirt water tube 49 as a firstfluid-flow connector connects a dirt water container outlet 10 with theupstream side of the filtration unit 5. A flexible hose 11 as a thirdfluid-flow connector connects the backwash bulb 7 with the downstreamside of the filtration unit 5. When the backwash bulb 7 is compressed,clean water from inside the backwash bulb 7 is pressed backwards throughthe membrane into the upstream side in the filtration unit 5 and throughupstream outlet 23 out of the housing 5′ of the filtration unit 5 andinto a flexible backwash tube 12, the distant end of which is connectedto the upper part of the backwash receptacle 8 for receiving thebackwash water with the particulate and biological matter from thebackwash action.

In the case that the microporous membrane filter is a bundle of hollowfibre membrane filters, optionally, the fibres are pottet at both endsand have an inside-out flow for filtration. In this case, biofilmformation and accumulation of particles occurs inside the hollow fibres.Examples of likewise principles are disclosed in WO2008/110166 andWO2008/110172.

Actually, the backwash tube 12 also works as a vent tube in having avent opening at its uppermost part 13, where it bends. Alternatively,instead of using a single tube for venting as well as for backwashwater, two separate tubes may be provided, one for venting and one forthe backwash water.

When dirt water from the dirt water container 2 enters the upstream sidein the filtration unit 5, air resident on the upstream side of thefiltration unit 5 is pressed along the membrane and out of thefiltration unit 5 and into the vent tube/backwash tube 12, after whichthe air in the vent tube 12 is followed by dirt water from the upstreamside of the filtration unit 5. The dirt water in the vent tube 12 willrise to the same level as the dirt water in the dirt water container 2.For this reason, the uppermost part 13 with the vent opening in the venttube 12 should be above the normal maximum level of the dirt water inthe dirt water container 2. For this reason, the location of the ventopening is near the upper edge 14 of the dirt water container 2, whichis less than 5 cm from the upper edge 14, or rather 1-2 cm from theupper edge 14, as illustrated. However, the uppermost part 13 with thevent opening could also be above the edge of the dirt water container 2.

FIG. 1C is a drawing with a cut-away of a portion of the device 1. Asillustrated, the dirt water container 2 has an elevated outlet 15, forexample 1-3 cm, above the bottom 16 of the dirt water container 2. Thisway, it is assures that the heaviest particulate matter is collected atthe bottom 16 of the dirt water container 2 and prevented from enteringthe dirt water tube (shown with reference 49 in FIG. 1B) and enteringthe filtration unit 5 through upstream inlet 19 of the filter housing 5.The dirt water container 2 is covered by a lid 17 which has a slopingsurface towards an entrance opening which is closed by a closure member18. The downwards sloping surface of the lid 17 acts as a funnel whenfilling water into the dirt water container 2 when the closure member 18is removed. Also, the lid 17 is removable for cleaning purposes.

The dirt water container 2 may, advantageously, comprise a coarse filterat its fluid inlet. A further option for the device is an antimicrobialsource in the dirt water container, for example a halogen source. Achlorine tablet is one option for a halogen source.

As illustrated in FIG. 1C, the clean water tank 3 has an enclosure thatis entirely closed and sealed against the environment apart from a tap(shown as reference 24 in FIG. 1D) for dispensing of water from theclean water tank 2 through the tap 24. However, alternatively, it may beprovided openable, for example by a lid, in order to give access to theclean water tank for cleaning.

It should be noted that the clean water tank 3 has a sloping uppersurface 33 in order not to accumulate water that may have been spilledon the surface 33.

As illustrated in FIG. 1D, the device 1 is compact due to its modularbuild-up with the mutually stacked dirt water container 2, intermediatemodule 4, and clean water tank 3. The stacked principle is aestheticallyattractive, minimizes accumulation of dirt around the tubing and thefiltration unit 5 and also allows an easy cleaning of the device 1.

FIG. 2 is an exploded drawing illustrating some of the above mentionedfeatures in more detail. In addition, is illustrates an agent reservoir31, in which a source for an agent is added to the clean water in theclean water tank 3. Examples of an agent are nutrients, pharmaceuticals,or antimicrobials, or combinations thereof. This agent reservoir 31 isprovided inside the clean water tank 3. Clean water from the filtrationunit 5 flows into the agent reservoir 31 and enriches the water bydissolving a slow-soluble matrix in side the agent reservoir 31. Forexample, the matrix contains an agent that is liberated upon dissolutionof the matrix.

In order for microbes not to proliferate inside the clean water tank 2,the internal walls of the clean water tank 2 may be provided with anantimicrobial surface. Non-limiting examples of antimicrobials for suchpurpose are silver and quaternary ammonium, both having the advantage ofbeing long lasting. Further examples are given in International patentapplication WO2008/067817.

The dirt water container 2 comprises on its outer side a set of snap-onconnectors 21 for the vent tube/backwash tube 12. The vent tube 12 has avent opening 22 at its uppermost part 13, where it is bent.

A distributor 25 is attached to the upper part of the filtration unitand received water from the downstream side through an opening in thefilter housing 5′, the opening working as a downstream outlet of cleanwater. It receives clean water from the downstream side for distributioninto the clean water tank 3 and into the backwash bulb 7. It is alsoconfigured to prevent the water from the bulb 7 entering the clean watertank 3 during backwash as it comprises a check valve that blocks thefluid passage between the backwash bulb 7 and the clean water tank 3during backwash.

As it appears from the drawing, the distributor 25 is located attachedto the upper side of the filtration unit 25. As the water exits from thedownstream side of the filtration unit 5 at the top of the filtrationunit 5 above the membrane in the filtration 5 unit, the filtration unit5 is not drained, thus, minimizing the risk for drying out of the porousmembrane in the filtration unit 5, which is important for polymermembranes, such as hollow fibre membranes, because a drying out can leadto collapse of the membrane pores.

For an alternative embodiment, it should be mentioned that the filterhousing 5′ could also be connected to the distributor 25 through a tube.

As illustrated in FIG. 3A, the distributor 25 also comprises a ventvalve 28A for venting air from the sealed clean water tank 3 when waterenters the tank 3 from the filtration unit 5. In FIG. 3B, a vent channel28B is shown, which received the air and which is in connection with thevent valve 28A. Also shown in FIG. 3B and FIG. 3C is the inlet channel29 for receiving filtered water from the downstream side through thedownstream outlet 29A and into the distributor 25. This filtered waterfrom the downstream side is distributed either through the firstdistributor outlet 20 for feeding into the backwash bulb 7 or throughsecond distributor outlet 30 for feeding into the clean water tank 3.

As illustrated in FIGS. 3A and 3C, the distributor 25 also comprises aball valve housing 26 with ball 26B. The opening 26A seen on top of theball valve housing 26 in FIG. 3A is only used during assembly forplacing a ball 31 inside the valve housing 26 and would normally becovered by a plate 27 as illustrated in FIG. 3C. Inside the ball valvehousing 26, a ball 26B is provided for sealing against valve seat 32when pressure is exerted on the ball 26B from pressurised backwash waterflowing into the ball valve housing 26 from the backwash bulb 7backwards through the second filter housing outlet 20.

Under normal operational conditions, gravity forces water from the dirtwater container 2 through the membranes in the filtration unit 5 andinto the downstream side of the filtration unit 5. From the downstreamside of the membrane in the filtration unit 5, filtered water enters thedistributor 25 through an inlet channel 29. Through the distributor, thewater will first flow into the first distributor outlet 20 and fill thebackwash bulb 7 before the water slowly under low pressure flows throughthe ball valve housing 26A and into the second distributor outlet 30 andfurther into the clean water tank 3. During this low pressure flow, theball 26B floats on top of the water in the ball valve housing 26. If thebackwash bulb 7 is compressed, the water from the bulb 7 will flowbackwards through the first distributor outlet 20 and into the inletchannel 29. As, the compression of the bulb 7 causes a flow speed of thebackwash water much higher than the normal flow speed of the water fromthe filtration unit under normal gravity filtering conditions, the waterpresses the ball 26B in the ball valve housing 26 against the seat 32,preventing water to enter the second distributor outlet for the cleanwater tank 2. Instead, the backwash water flows into the downstream sideinside the filtration unit 5 and exerts backwash pressure on themembrane for forcing clean water from the bulb 7 backwards through themembrane pores. The ball valve system is a simple arrangement thatguides the backwash water to the correct location without the necessityof interference by the user apart from compressing the backwash bulb 7.

When the backwash water is pressed into the downstream side of themembrane in the filtration unit 5 and further backwards through themembrane into the upstream side of the filtration unit 5, a check valve(not shown), for example a corresponding one way ball valve, preventsthe backwash water to enter the tube 49 to the dirt water tank 2, seeFIG. 2 in this respect. Instead, the backwash water exits the upstreamoutlet 23 for flowing through backwash tube (vent tube) 12, 12A and intothe backwash receptacle 8. The backwash receptacle 8 minimizes the riskof users drinking the backwash water by mistake.

For example, the device of FIG. 3 comprises a selection or all of thefollowing features in combination,

-   -   the clean water tank has an enclosure sealed against the        environment,    -   the dirt water container is arranged at least 10 cm above the        clean water tank,    -   the filtration unit is arranged in a space above the clean water        tank and below the dirt water container,    -   the porous filtration membrane is an ultrafiltration membrane or        microfiltration membrane,    -   the membrane is a bundle of hollow microporous fibres;    -   the space is defined by an intermediate module having cross        sectional dimensions in the horizontal plane corresponding to        cross sectional dimensions of the dirt water container and the        clean water tank,    -   the intermediate module is supported by the clean water tank        and, in turn, supports the dirt water container when in stacked        conditions,    -   the dirt water container, the intermediate module and the clean        water tank in such stacked conditions form an integrated        three-module system,    -   the first flow connector comprises a tube,    -   the filtration unit is oriented with the longitudinal axis        within less than 10 degrees from a horizontal plane, and    -   the device is portable.

FIGS. 4A and 4B illustrate an embodiment that can be decreased in sizefor storage or transport. This device comprises a dirt water container 2and a clean water tank 3 and a filtration unit 5 as explained above, aswell as backflush bulb 7 and backwash receptacle 8. As an option, thedirt water container 2 also has an upper coarse filter 34. Thefiltration unit 5 is inserted into a corresponding compartment 41 andcovered by a lid 35 which is fastened to the clean water tank 3 by snapconnectors 40.

The dirt water container 2 is connected to the clean water tank 3 by aconnector 36. The connector has an upper platform 39 for supporting thedirt water container 2. This connector has profiles 37 that slidinglycooperate with grooves 38 in the outer side of the clean water tank 3 ina telescopic manner By pushing the connector 36 downwards with theprofiles 37 sliding in the grooves 38, the platform 39 is lowered untilit rests upon lid 35. This is a good position for the connector duringstorage, because the volume of the device is decreased and it is morestable. For use, the connector 36 with the platform 39 is pulled awayfrom the clean water tank 3 until a maximum height. This height may besecured by a snap lock, for example. The advantage of the greaterdistance between the dirt water container 2 and the clean water tank 3is a higher gravity pressure on the water. For portable models of thedevice as illustrated in FIG. 4, the height of the connector istypically between 10 and 50 cm, for example between 15 and 30 cm.

In a further embodiment, the dirt water container 2 is made of aflexible, collapsible material and can be pressed into a flat structuretaking up very little volume, which decreased the volume even furtherfor transport and storage.

FIG. 4C illustrates the tubing including the dirt water tube 49 from thedirt water container to the filtration unit 5, the vent tube 12 with theextension 12A to the backwash receptacle 8, and the tube between thedistributor 25 and the backwash bulb 7.

FIG. 4D is a cross sectional drawing of the device 1, which illustratesthe backwash receptacle 8 having an opening 8A for receiving backwashwater. In addition, it comprises a number of smaller holes 8B around theopening 8A, which makes it difficult to drink from the backwashreceptacle 8 and indicates for the user that the water in the backwashreceptacle is not intended for consumption. In addition, the opening 8Ais provided lower than the upper surface 8C of the backwash receptacle8, such that it is difficult to pair the opening 8 with lips from amouth of a user for drinking.

FIG. 5A-D illustrate an embodiment that can be decreased in size forstorage or transport. FIG. 5A illustrates an assembled drawing, FIG. 5Ban exploded drawing, FIG. 5C illustrates the tubing, and FIG. 5D shows acollapsed state of the device. This device comprises a dirt watercontainer 2 and a clean water tank 3 and a filtration unit 5 asexplained above, as well as backflush bulb 7 and backwash receptacle 8.The dirt water container has a lid 17 with a coarse filter 34. Thefiltration unit 5 is inserted into a corresponding compartment 41. Oncethe filtration unit 5 inserted into the compartment 41, the clean watertank is covered by a lid 35 which is fastened to the clean water tank 3.

The dirt water container 2 is connected to the clean water tank 3 by aconnection 36′. The connection 36′ is connected to the dirt watercontainer 2 by first a rotatable hinge 42, best seen in FIG. 5A, withtwo cooperating hinge parts 42A and 42B, best seen in FIG. 5B, andconnected to the clean water container 3 by a second hinge comprising athird hinge part 43 and a sliding groove 44. By rotating the connection36′ in the hinges 42 and due to the third hinge part 43 in cooperatinggroove 44, the dirt water container 2 is lifted upwards relatively tothe clean water tank 3 and can likewise be lowered in order to take upless space. In order to stabilize the connection 36′, it comprises twoconnection parts 47, 48. The second part 48 is hinged by the fourthhinge part 45 in bushing 46. The first and the second connection parts47 and 48 are also mutually hinged by hinge part 50 and a correspondingcooperating hinge part (not shown) in the second connection part 48.

When the dirt water container 2 is lowered by a scissor action of thetwo connection parts 47, 48, it may also be rotated in addition aroundthe hinge 42 and, when the lid 17 is removed, through its opening 2Aembrace partly the clean water tank 3 in the volume of the dirt watercontainer 2, as it is illustrated in FIG. 5D. This adds to thecompactness for storage and transport and protects the tap 24 againsttransport damage.

In FIG. 5A, the vent tube and the tube connections between the dirtwater container 2 and the filtration unit 5 and further to the backwashbulb 7 and the backwash receptacle 8 are not illustrated in detail butare similar to the embodiment in FIG. 1 and FIG. 2. Optionally, also,the distributor as illustrated in FIG. 3 may be applied for theembodiments of FIGS. 4 and 5.

FIG. 5C illustrated the possible tubing for the FIG. 5A embodiment inline with the tubing in the embodiment as explained for FIG. 2, wheretubing 49 connects the dirt water container 2 with the filtration unit5, tubing 11 connects the distributor 25 of filtration unit 5 with thebackwash bulb 7, and tubing 12 is a vent/backwash tube extended withtubing 12A into the backwash receptacle 8.

FIG. 6 illustrates a slightly amended embodiment relatively to theembodiment of FIG. 5, where the backwash bulb 7 and the backwashreceptacle 8 are differently oriented. The backwash bulb 7 is fastenedpermanently to the device such that it is not removable, whichsimplifies the handling of the device even further, because it can beeasily compressed in the shown location.

For example, the devices above comprises a combination of the followingfeatures,

-   -   the clean water tank has an enclosure sealed against the        environment,    -   the dirt water container is arranged at least 10 cm above the        clean water tank,    -   the filtration unit is arranged in a space above the clean water        tank and below the dirt water container,    -   the porous filtration membrane is an ultrafiltration membrane or        microfiltration membrane,    -   the porous filtration membrane is a bundle of hollow fibre        membranes    -   the intermediate module is supported by the clean water tank        and, in turn, supports the dirt water container when in stacked        conditions,    -   the first flow connector comprises a tube,    -   the filtration unit is oriented with the longitudinal axis        within less than 10 degrees from a horizontal plane, and    -   the device is portable.

Exemplary, non limiting dimensions for the device as described above andaccording to the claims are as follows. The volumes of the dirt watercontainer and the clean water tank are between 5 and 30 litres or 5 and20 litres, for example between 8 and 12 litres. The length of thefiltration unit is between 10 and 50 cm. The height of the intermediatemodule is between 10 and 40 cm. In case that a bundle of hollow fibremembranes is used for the filtration unit, the number of fibres isbetween 50 and 400 and the cross sectional outer diameter of each fibreis between 1 and 3 mm.

It should be mentioned that the above embodiments described in relationto the drawings can be modified by exchanging the filtration unit withother purification units, for example comprising resins for chemicalpurification as well as adsorption media. In such cases, the aspects ofthe vent tube and the backwash bulb and receptacle may be avoided,however, keeping the overall technical solution of the interplay betweenthe dirt water container (2), the clean water tank (3) and theintermediate module (4), as described in FIGS. 1 and 2, or thetelescopic arrangement as described in FIG. 4, or the rotational meansfor collapsing the device, as illustrated in FIGS. 5 and 6.

FIGS. 7A and 7B illustrate a possible embodiment for a filtration module5. The upstream inlet 19 and the upstream outlet 23 are arrangeddifferently that in the embodiment of FIG. 2 but has the same effect.Through the upstream inlet 19, water from the dirt water container (notshown) enters the filtration module 5 into the upstream side 52. Air andwater can exit the upstream side 52 through upstream outlet 23. The dirtwater is enters the inner channels of the microporous hollow filtrationmembranes 50, which are potted at both ends in a polymer potting 51, andis filtered in an inside out flow into the downstream side 53. From thedownstream side 53, it enters distributor 25 and exits the distributorthrough first distributor outlet 20 into a backwash bulb (not shown) andthrough second distributor outlet 30 into the clean water tank (notshown). The distributor's ball valve system with ball 26B is explainedin connection with FIG. 2.

During backwash, clean water is pressed backwards through the membrane50 bundle from the downstream side 53 into the upstream side 54, and thewater with the particles that are removed from the hollow fibre membrane50 bundle leaves the upstream side 52 through upstream outlet 23. A ballvalve 54 with ball 55 prevents the backwash water to flow back into thedirt water tank (not shown).

FIG. 8a is a drawing of an alternative embodiment, where the backwashreceptacle 8 is provided at the side of the dirt water container 2. Alever 56 is used for backwashing. FIG. 8b shows the interior units ingreater detail. The water flow is as follows. Water from the dirt watercontainer 2 enters entrance openings 62 in a cover 61 of anantimicrobial unit 60 for picking up a small concentration ofantimicrobials that prevent proliferation of microbes in the filtrationunit 5. From the antimicrobial unit 60, the dirt water enters a tube 49that connects the dirt water container 2 with the upstream inlet 19 ofthe filtration unit 5. The filtration unit 5 is arranged vertically orat an angle slightly deviating from vertical. However, the filtrationunit 5 could also be arranged at a different orientation, for examplehorizontally or at an angle slightly deviating from horizontally.

A non-limiting but useful example of a filtration unit 5 is illustratedin FIG. 10. Water enters the upstream inlet 19 and flows throughrun-down channel 69 to the bottom of the filtration unit 5. From thisupstream side 52, the dirt water enters U-bent hollow membrane fibres68, which are potted 51 at both ends in a resin. The water enters themembranes 68 outside-in, and from the lumen of the membranes 68, thefiltered and clean water is released from the downstream side 53 at theupper end of the filtration unit 5.

As illustrated in FIG. 9, the water flows from the upper end of thefiltration unit 5 into the distributor 25 and through first distributoroutlet 20 into lever tube 57, which in turn is fluid-flow connected tothe backwash bulb 7. Once, backwash bulb 7 is filled with clean water,the clean water from the filtration unit 5 will fill the distributor 25further, and clean water will flow through the second distributor outlet30 into the clean water tank 3. Once, the clean water tank 3 is full, afloater 58 will rise and shut off flow from second distributor outlet 30in order to prevent overfilling of the clean water tank 3. Thedistributor 25 comprises a ball 26B which will allow water to passaround the ball 26B and into the second distributor outlet 30 if thepressure of the water is low, which means that the water is flowing bygravity force through the system. However, when the bulb 7 is compressedfor backwash, the backwash compression raises the water pressure in thedistributor 25, and the ball 26B is pressed against the ball seat 32 andwill thereby close off the second distributor outlet 30. Instead, thecompression of the bulb 7 leads to backwash of the clean water inreverse through the membranes 68 in the filtration unit 5.

Returning to FIG. 8b , the lever 56 for compression of the backwash bulbis illustrated. The lever 56 is has a pivot mount 71 at the distributor25, adjacent to the upstream inlet 19 of the filter housing 5. The lever56 is operated manually or by foot by suppressing the handle 70. Thus,also in this case, the backwash bulb 7 is of the type that it ismanually compressible; however, by convenience, it is compressedmanually by the lever 56. In alternative embodiments, no lever ismounted, and the bulb 7 is to be compressed by hand directly.

During backwashing, the backwash water flows through the filtration unit5 in reverse, exits the filtration unit 5 at the upstream inlet 19 andflows backwards into the tube 49 that connects the dirt water container2 with the filtration unit 5.

The flow path is illustrated in greater detail in FIG. 11. In order toprevent the backwash water to reach the dirt water container 2, a checkvalve 54 with a ball 55 is arranged in the tube 49. When water flowsdownwards in the tube 49, during normal gravity filtering, water canpass around the ball 55. In contrast thereto, during back-wash, the ball55 is pressed upwards against its seat 55A and closes for the furtherflow upwards of the backwash water.

Instead, the backwash water leaves the tube 49 through a side exit 59,as illustrated in FIG. 8b . The side exit 59 from tube 49 has a tubeconnection (not shown) connected to the dirt water receptacle 8 forreceiving the backwash water from the tube 49.

The antimicrobial unit 60 is shown in greater detail in FIG. 11. Underthe cover 61, a sealed compartment 63 is provided for an antimicrobialsource 64. The sealed compartment 63 is sealed against water enteringthe sealed compartment 63. However, it is not hermetically sealed, as itis provided with a very narrow bottom pin hole 66 through whichantimicrobial can escape in gas form from the sealed compartment 64 andenrich the dirt water, for example to less than 1 ppm, for examplebetween 0.1 and 1 ppm. For example, the antimicrobial source 64 isprovided as a chlorine tablet which slowly evaporates out of the pinhole 66. The pin hole 66 is of a diameter preventing water to enter thepinhole due to surface tension of the water. For example, the diameteris in the range of 0.6-1.5 mm In order to secure the pin hole furtheragainst water entering the sealed compartment 63, the pin hole isoptionally provided with a hydrophobic surface.

As an alternative or additional measure to protect the antimicrobialsource, for example chlorine tablet, from contact with water, but allowevaporation thereof, the antimicrobial source can be enclosed by a gaspermeable but water impermeable enclosure. For example, such enclosureis a porous hydrophobic material. Examples of such materials arehydrophobic, open celled foams or hydrophobic woven or non-wovenfabrics.

Aspects

In the following a number of interrelated aspects are described.

Aspect 1. A device (1) for water purification, the device (1) comprisinga dirt water container (2) for accumulating dirt water and apurification unit (5) for purifying the dirt water, wherein the dirtwater container (2) is arranged above the purification unit (5) fordriving water through the purification unit (5) by gravity;

wherein the purification unit (5) comprises a filter housing (5′)enclosing a purification medium that is separating an upstream side ofthe purification unit (5) from a downstream side of the purificationunit (5) such that water in the purification unit (5) can flow from theupstream side to the downstream side only through the purificationmedium;wherein the dirt water container (2) has a container outlet (10), andthe filter housing (5′) has an upstream inlet (19) to the upstream side,wherein the container outlet (10) and the upstream inlet (19) arefluid-flow-connected by a first flow connector (9) for receiving dirtwater from the dirt water container (2) into the upstream side of thepurification unit (5);wherein the device comprises a clean water tank (3) fluid-flow connectedto the downstream side through a downstream outlet (29A) for receivingpurified water from the downstream side.

Aspect 2. A device according to aspect 1, wherein the purification unit(5) is a filtration unit (5) and the purification medium is amicroporous filtration membrane.

Aspect 3. A device according to aspect 2, wherein the filtration unit(5) has an upstream outlet (23) in the filter housing (5′) for outlet offluid from the upstream side, wherein a vent tube (12) is connected tothe upstream outlet (23), the vent tube (12) extending up-wards andhaving a vent opening (22) into atmosphere for venting of air from theup-stream side, wherein the vent opening (22) is provided at a levelcloser to a top than to a bottom (16) of the dirt water container (2).

Aspect 4. A device according to aspect 3, wherein the vent opening (22)is provided at a ref-erence height, the reference height being at most 5cm from an upper edge (14) of the dirt water container (2).

Aspect 5. A device according to aspect 3 or 4, wherein the vent tube(12) extends upwards outside the dirt water container (2) and outsidethe clean water tank (3) and has a vent opening (22) into atmosphereoutside the dirt water container (2).

Aspect 6. A device according to aspect 5, wherein an upper part (25) ofthe vent tube (12) is attached to an outer side of the dirt watercontainer (2).

Aspect 7. A device according to any one of the aspects 3-6, wherein thedevice comprises a manually compressible backwash bulb (7) that isfluid-flow connected to the down-stream side for receiving of cleanwater in the backwash bulb (7) for backwash pur-poses; wherein abackwash tube (12, 12A) is provided which is connected to the up-streamside for receiving contaminated backflush water and connected to abackwash receptacle (8) for dispensing the contaminated backwash waterinto the backwash re-ceptacle when water is pressed from the downstreamside through the membrane to the upstream side by compression of thebackwash bulb and further from the upstream side through the backwashtube (12, 12A) into the backwash receptacle (8), wherein the backwashtube (12, 12A) is an integral part of the vent tube (12) for venting airfrom the upstream side and dispensing backwash water through the sametube (12, 12A).

Aspect 8. A device according to aspect 2, wherein the device comprises amanually compressible backwash bulb (7) that is fluid-flow connected tothe downstream side for receiving of clean water in the backwash bulb(7) for backwash purposes; wherein a back-wash tube (12, 12A) isprovided which is connected to the upstream side for receivingcontaminated backflush water from the filtration unit (5) and connectedto a backwash receptacle (8) for dispensing the contaminated backwashwater into the backwash receptacle when water is pressed from thedownstream side through the membrane to the upstream side by compressionof the backwash bulb and further from the upstream side through thebackwash tube (12, 12A) into the backwash receptacle (8).

Aspect 9. A device according to aspect 7 or 8, wherein the backwash tube(12A) is connected to the backwash receptacle (8) through a fluidentrance (8A) of the backwash receptacle, the fluid entrance beingsurrounded by multiple holes 8B for preventing drinking therefrom.

Aspect 10. A device according to any one of the aspects 7-9, wherein thebackwash receptacle (8) is provided at a level lower than the filtrationunit (5).

Aspect 11. A device according to any one of the aspects 7-10, wherein aone way check valve is provided between the dirt water container (2) andthe upstream side of the filtration unit (5) for preventing backwashwater to be pressed into the dirt water container (2).

Aspect 12. A device according to any one of the aspects 3-11, whereinthe filtration unit (5) is elongate tubular with a longitudinal axisthat is horizontal or oriented at most 45 degrees from a horizontalplane when the filtration unit (5) is in proper orientation for waterfiltration.

Aspect 13. A device according to aspect 12, wherein, when the filtrationunit (5) is in proper orientation for water filtration, filtered wateris dispensed from the downstream side through a downstream outlet (29A),wherein the downstream outlet (29A) is provided at a level above anyuppermost microporous surface of the microporous filtration membrane formaintaining a water level in the filtration unit (5) above the uppermostmicroporous surface.

Aspect 14. A device according to aspect 2, wherein the filtration unit(5) is elongate tubular with a longitudinal axis that is horizontal ororiented at most 45 degrees from a horizontal plane when the filtrationunit (5) is in proper orientation for water filtration, wherein, whenthe filtration unit (5) is in proper orientation for water filtration,filtered water is dispensed from the downstream side through adownstream outlet (29A), wherein the downstream outlet (29A) is providedat a level above any uppermost microporous surface of the microporousfiltration membrane for maintaining a water level in the filtration unit(5) above the uppermost microporous surface.

15. A device according to any one of the aspects 12-14, wherein thelongitudinal axis that is horizontal or oriented at most 10 degrees froma horizontal plane when the filtration unit (5) is in proper orientationfor water filtration,

Aspect 16. A device according to any one of the aspects 2-13, whereinthe device (1) comprises a distributor (25), the distributor (25)comprising an inlet channel (29) for receiving filtered water from thedownstream side, a first distributor outlet (20) for dispensing filteredwater to a compressible backwash bulb (8), and a second distribu-toroutlet (30) for providing filtered water into the clean water tank (3),the distributor (25) further comprising a one-way check valve (26A, 26B,32) arranged between the first distributor outlet (20) and the seconddistributor outlet (30) for preventing back-wash water from thecompressible backwash bulb from entering the clean water tank (3) whenwater is forced backwards through the first distributor outlet (20) dueto compression of the backwash bulb (8).

Aspect 17. A device according to aspect 16, wherein the check valve is aball valve, comprising a valve housing (26A) containing a ball (26B) andwith a ball seat (32) in a wall of the valve housing (26A) on a sideadjacent to the second distributor outlet (30) and remote to the firstdistributor outlet (20).

Aspect 18. A device according to any one of the aspects 2-17, whereinthe filtration unit (5) comprises a plurality of microporous hollowfibre membranes.

Aspect 19. A device according to aspect 18, wherein the hollow fibremembranes are arranged in parallel and potted at both ends in a resin.

Aspect 20. A device according to aspect 18 or 19, wherein the filtrationunit comprises an additional filtration medium downstream of the hollowfibre membranes, the addition-al filtration medium being a fibrousmatrix containing electropositive adsorptive nano-particles.

Aspect 21. A device according to aspect 20, wherein the hollow fibremembranes are microfiltration membranes.

Aspect 22. A device according to any preceding aspect, wherein the dirtwater container (2) is arranged above the clean water tank (2) and witha clearance of at least 5 cm between the clean water tank (3) and thedirt water container (2).

Aspect 23. A device according to any preceding aspect, wherein the cleanwater tank has an upper, closed top and the dirt water container has aclosed bottom, and wherein the purification unit is arranged between theclosed top of the clean water tank and the closed bottom of the dirtwater container (2).

Aspect 24. A device according to any preceding aspect, wherein thepurification unit (5) is arranged only in a space outside and above theclean water tank (3) and only outside and below the dirt water container(2).

Aspect 25. A device according to any preceding aspect, wherein thedevice is a portable device with dry weight of less than 30 kg, with avolume of the dirt water container of less than 30 litres, and with avolume of the clean water tank of less than 30 litres.

Aspect 26. A device according to any preceding aspect, wherein the cleanwater tank (2) has an enclosure sealed against the environment.

Aspect 27. A device according to any preceding aspect, wherein thedevice (1) has a connection (36, 36′) between the clean water tank (3)and the dirt water container (2), the connection (26, 26′) comprisingmeans (37, 38, 47, 48) for varying the distance be-tween the clean watertank (3) and the dirt water container (2).

Aspect 28. A device according to aspect 27, wherein the connection (36,36′) has a first state where the clean water tank (3) and the dirt watercontainer (2) are in a close position, which is a storage or transportstate, and the connection (36, 36′) has a second state where the cleanwater tank (3) and the dirt water container (2) are in a remotecondition, which is an operational condition for water filtration, wherethe distance between the clean water tank and the dirt water containerin the second condition is between 5 cm and 100 cm larger than in theclose position.

Aspect 29. A device according to aspect 27 or 28, wherein the means forvarying the distance comprises a set of profiles (37) in slidingcooperation with the outer side (38) of the clean water tank (3) or theouter side of the dirt water container (2) or both.

Aspect 30. A device according to aspect 29, wherein the clean water tank(3) has grooves (38) on its outer side which take up the profiles (37)in sliding cooperation.

Aspect 31. A device according to aspect 27 or 28, wherein the means forvarying the distance comprises a rotationally hinged (42) profile (47)with an angle varying relatively to the clean water tank (3) independency of the distance between the clean water tank (3) and the dirtwater container (2).

Aspect 32. A device according to aspect 31, wherein the profile (47) ishinged in a first hinge (43, 44) at the clean water tank (3) and ishinged in a second hinge (42) at the dirt water container (3).

Aspect 33. A device according to aspect 31 or 32, wherein the dirt watercontainer (2) has an upper opening (2′) which is dimensioned larger thana cross section of the clean water tank in order to partly enclose theclean water tank inside the dirt water contain-er (3) in storagecondition

Aspect 34. A device according to any one of the aspects 1-26, wherein anintermediate module (4) is provided having a cross sectional dimensionin the horizontal plane corresponding to cross sectional dimensions ofthe dirt water container (2) and the clean water tank (3), wherein theintermediate module (4) is supported by the clean water tank (3) and, inturn, supports the dirt water container when in stacked conditions,wherein the dirt water container (2), the intermediate module (4) andthe clean water tank (3) in such stacked conditions form an integratedthree-module system

NUMBER LIST

-   1—device-   2—dirt water container-   3—clean water tank-   4—intermediate module-   5—filtration unit-   5′—filter housing-   6—cavity in clean water tank enclosure for backwash bulb-   7—backwash bulb-   8—backwash receptacle-   8A—opening in the backwash receptacle for receiving backwash water-   8B—holes surrounding the opening 8A-   8C—upper surface of backwash receptacle 8-   9—cavity in clean water tank enclosure for backwash receptacle-   10—container outlet-   11—hose between backwash bulb 7 and filtration unit 5 (third flow    connector)-   12—vent tube-   12A—backwash tube-   13—uppermost part of the backwash tube/vent tube-   14—upper edge of dirt water container-   15—elevated part of container outlet-   16—bottom of dirt water container-   17—lid of dirt water container-   18—closure member in lid 17-   19—upstream inlet in filter housing-   20—first distributor outlet from distributor to backwash bulb 7-   21—snap connectors for vent tube 12-   22—vent opening-   23—upstream outlet from filter housing-   24—tap-   25—distributor (second flow connector)-   26—valve housing-   26A—valve opening covered by cover 27-   26B—ball-   27—cover for opening 26A of ball valve housing 26-   28A—vent valve-   28B—vent valve channel-   29—inlet channel in distributor-   29A—downstream outlet from outlet side-   30—second distributor outlet from distributor 25 to clean water tank    3-   31—agent reservoir-   32—ball seat-   33—sloping upper surface of clean water tank 3-   34—prefilter-   35—lid of clean water tank 3-   36—connector-   37—connector profile-   38—grooves in clean water tank 3 cooperating with connector profile    37-   39—platform support for dirt water container 2-   40—snap connectors of lid 35-   41—compartment for filtration unit 5 on top of clean water tank 3-   42—hinge between connection 36′ and dirt water container 2-   42A, 42B—first and second hinge parts between connection 36′ and    dirt water container 2-   43—third hinge part between connection 36′ and dirt water tank 2-   44—groove in lid 35 for third hinge part 43-   45—fourth hinge part between lid 35 and second part 48 of connection    36′-   46—bushing in clean water lid 35 for fourth hinge part 45-   47—first part of connection 36′-   48—second part of connection 36′-   49—tube between dirt water tank 2 and filtration unit 5 (first flow    connector)-   50—hollow fibre microporous membranes, for example microfiltration    membranes-   51—potting of the membranes-   52—upstream side-   53—downstream side-   54—check valve for preventing backflow into dirt water container 2-   55—ball for check valve 54-   55A—seat for ball 55-   56—lever for compressing backwash bulb 7-   57—lever tube between backwash bulb 7 and filtration unit 5 (third    flow connector)-   58—floater for shutting off flow from second distributor outlet 30-   59—side exit from tube 49 for connection to dirt water receptacle 8-   60—antimicrobial unit for adding antimicrobial to the dirt water-   61—cover of antimicrobial unit 60-   62—dirt water entrance openings of antimicrobial unit 60-   63—sealed compartment for antimicrobial source 64-   64—antimicrobial source-   65—bottom of sealed compartment 63-   66—pinhole in bottom 65 of sealed compartment-   67—channel from upstream inlet 19 of filter housing 5′ to opposite    end-   68—U-bent hollow membrane fibres-   69—run down channel in filtration unit 5-   70—handle of the lever 56.

1-25. (canceled)
 26. A portable device (1) for water purification, the device (1) comprising a dirt water container (2) for accumulating dirt water and a purification unit (5) for purifying the dirt water, wherein the dirt water container (2) is arranged above the purification unit (5) for driving water through the purification unit (5) by gravity; wherein the purification unit (5) comprises a filter housing (5′) enclosing a purification medium that is separating an upstream side (52) of the purification unit (5) from a downstream side (53) of the purification unit (5) such that water in the purification unit (5) can flow from the upstream side (52) to the downstream side (53) only through the purification medium; the filter housing (5′) having a downstream outlet (29A) from the downstream side (53); wherein the purification unit (5) is a filtration unit (5) and the purification medium is a microporous filtration membrane; wherein the dirt water container (2) has a container outlet (10), and the filter housing (5′) has an upstream inlet (19) to the upstream side, wherein the container outlet (10) and the upstream inlet (19) are fluid-flow-connected by a first flow connector (9) for receiving dirt water from the dirt water container (2) into the upstream side of the purification unit (5); wherein the device comprises a clean water tank (3) fluid-flow connected to the downstream side (53) through the downstream outlet (29A) for receiving purified water from the downstream side (53).
 27. A device according claim 26, wherein the device (1) comprises a compressible backwash bulb (7) and a distributor (25) upstream of the backwash bulb (7), the distributor comprising an inlet channel (29) fluid-flow connected to the downstream outlet (29A) for receiving clean water from the downstream side (53) through the downstream outlet (29A); the distributor (25) comprising a first distributor outlet (20) fluid-flow connected to a compressible backwash bulb (7) and configured for dispensing filtered water only to the compressible backwash bulb (7) and not into the clean water tank (3), the compressible backwash bulb (7) being arranged for backwashing of the microporous filtration membrane in reverse direction through the first distributor outlet (20) by compression of the compressible backwash bulb (7); the distributor (25) comprising a second distributor outlet (30) fluid-flow connected to a clean water tank (3) for providing filtered water only into the clean water tank (3); the distributor (25) further comprising a one-way check valve (26A, 26B, 32) arranged between the first distributor outlet (20) and the second distributor outlet (30) for preventing backwash water from the compressible backwash bulb (7) from entering the clean water tank (3) when water is forced backwards through the first distributor outlet (20) due to compression of the backwash bulb (7) wherein the device is configured for flow of water from the downstream side (53) through the distributor (25) into the clean water tank (3) bypassing the backwash bulb (7).
 28. A device according to claim 27, wherein the second distributor outlet (30) is different and remote from the inlet channel (29) and different and remote from the first distributor outlet (20).
 29. A device according to claim 27, wherein the distributor is arranged for flow of filtered water from the distributor inlet channel (29) into the distributor (25) and arranged for distribution thereof either through the first distributor outlet (20) into the compressible backwash bulb (7) or through the second distributor outlet (30) into the clean water tank (3) bypassing the backwash bulb (7).
 30. A device according to claim 29, wherein the distributor (25) is arranged for distributing the water from the inlet channel (29) first into the first distributor outlet (20) for filling the backwash bulb (7) before distributing the water through the second distributor outlet (30) into the clean water tank
 3. 31. A device according to claim 27, wherein the check valve is a ball valve, comprising a valve housing (26A) containing a ball (26B) and with a ball seat (32) in a wall of the valve housing (26A) on a side adjacent to the second distributor outlet (30) and remote to the first distributor outlet (20).
 32. A device according to claim 31, wherein the ball (26B) is arranged for floating on top of the water in the ball valve housing 26 during filling of the clean water tank (3).
 33. A device according to claim 32, wherein the distributor (25) is configured for preventing water to enter the second distributor outlet (30) during backwash when backwash water from the bulb (8) is pressing the ball (26B) in the ball valve housing (26) against the ball seat (32).
 34. A device according to claim 26, wherein a backwash tube (12, 12A) is provided which is connected to the upstream side (52) for receiving contaminated backwash water from the upstream side (52) of the filtration unit (5) and connected to a backwash receptacle (8) for dispensing the backwash water into the backwash receptacle (8) when water is pressed from the downstream side (53) of the filtration unit (5) through the membrane to the upstream side (52) by compression of the backwash bulb (7) and further from the upstream side (52) through the backwash tube (12, 12A) into the backwash receptacle (8); wherein the backwash receptacle (8) is different and separate from the dirt water container (2).
 35. A device according to claim 34, wherein a one way check valve (54) is provided between the dirt water container (2) and the upstream side (52) of the filtration unit (5) for preventing backwash water to be pressed into the dirt water container (2).
 36. A device according to claim 34, wherein the filtration unit (5) has an upstream outlet (23) in the filter housing (5′) for outlet of fluid from the upstream side, wherein a vent tube (12) is connected to the upstream outlet (23), the vent tube (12) extending upwards and having a vent opening (22) into atmosphere for venting of air from the upstream side, wherein the vent opening (22) is provided at a level closer to a top than to a bottom (16) of the dirt water container (2), wherein the backwash tube (12, 12A) is an integral part of the vent tube (12) for venting air from the upstream side and dispensing backwash water through the same tube (12, 12A).
 37. A device according to claim 26, wherein the filtration unit (5) has an upstream outlet (23) in the filter housing (5′) for outlet of fluid from the upstream side, wherein a vent tube (12) is connected to the upstream outlet (23), the vent tube (12) extending upwards and having a vent opening (22) into atmosphere for venting of air from the upstream side, wherein the vent opening (22) is provided at a level closer to a top than to a bottom (16) of the dirt water container (2).
 38. A device according to claim 26, wherein the dirt water container (2) is arranged above the clean water tank (2) and with a clearance of at least 5 cm between the clean water tank (3) and the dirt water container (2).
 39. A device according to claim 26, wherein the dirt water container (2) is rigid.
 40. A device according to claim 26, wherein the clean water tank (3) is rigid.
 41. A device according to claim 26, wherein the device (1) has a modular build-up with mutually stackable dirt water container (2), intermediate module (4), and clean water tank (3), wherein the intermediate module (4) is supported by the clean water tank (3) and, in turn, supports the dirt water container (2) when in stacked condition to form an integrated three-module system.
 42. A device according to claim 26, wherein the dirt water container (2) is arranged above the clean water tank (2) and with a clearance of at least 5 cm between the clean water tank (3) and the dirt water container (2).
 43. A device according to claim 26, wherein the device is a portable device with dry weight of less than 30 kg, with a volume of the dirt water container of less than 30 liters, and with a volume of the clean water tank of less than 30 litres.
 44. A device according to claim 26, wherein the dirt water container (2) comprises an antimicrobial source.
 45. A device according to claim 44, wherein the antimicrobial source is a tablet containing releasable chlorine.
 46. A method for water purification with a portable device (1), the device (1) comprising a rigid dirt water container (2) for accumulating dirt water and a purification unit (5) for purifying the dirt water, wherein the dirt water container (2) is arranged above the purification unit (5) for driving water through the purification unit (5) by gravity; wherein the purification unit (5) comprises a filter housing (5′) enclosing a purification medium that is separating an upstream side of the purification unit (5) from a downstream side (53) of the purification unit (5) such that water in the purification unit (5) can flow from the upstream side to the downstream side only through the purification medium; the filter housing (5′) having a downstream outlet (29A) from the downstream side (53); wherein the purification unit (5) is a filtration unit (5) and the purification medium is a microporous filtration membrane; wherein the dirt water container (2) has a container outlet (10), and the filter housing (5′) has an upstream inlet (19) to the upstream side (53), wherein the container outlet (10) and the upstream inlet (19) are fluid-flow-connected by a first flow connector (9) for receiving dirt water from the dirt water container (2) into the upstream side of the purification unit (5); wherein the device comprises a clean water tank (3) fluid-flow connected to the downstream side through a downstream outlet (29A) for receiving purified water from the downstream side (53), wherein the device (1) comprises a distributor (25), the distributor comprising an inlet channel (29) connected to the downstream outlet (29A) for receiving clean water therefrom; the distributor (25) comprising a first distributor outlet (20) fluid-flow connected to a compressible backwash bulb (7) for dispensing filtered water to the compressible backwash bulb (7), the compressible backwash bulb (7) being arranged for backwashing of the microporous filtration membrane in reverse direction through the first distributor outlet (20) by compression of the compressible backwash bulb (7); the distributor (25) comprising a second distributor outlet (30) for providing filtered water into the clean water tank (3); the distributor (25) further comprising a one-way check valve (26A, 26B, 32) arranged between the first distributor outlet (20) and the second distributor outlet (30) for preventing backwash water from the compressible backwash bulb (7) from entering the clean water tank (3) when water is forced backwards through the first distributor outlet (20) due to compression of the backwash bulb (7), the method comprising providing a flow of water from the dirt water container (2) through the purification unit (5) and through the distributor inlet channel (29) into the distributor (25); providing a flow of water from the distributor through the first distributor outlet (20) into the compressible backwash bulb (7); filing the backwash bulb with water from the first distributor outlet (20) prior to distributing water from the second distributor outlet (30) into the clean water tank (3); after filling the backwash bulb stopping flow to the backwash bulb (7), after stopping the flow to the backwash bulb, providing a flow of water from the distributor (25) through the second distributor outlet (30) into the clean water tank (3) without distributing further water to the backwash bulb (7).
 47. A method according to claim 46, wherein the second distributor outlet (30) is different and remote from the inlet channel (29) and different and remote from the first distributor outlet (20).
 48. A method according to claim 46, wherein the check valve is a ball valve, comprising a valve housing (26A) containing a ball (26B) and with a ball seat (32) in a wall of the valve housing (26A) on a side adjacent to the second distributor outlet (30) and remote to the first distributor outlet (20), the method comprising causing the ball (26B) to float on top of the water in the ball valve housing 26 during filling of the clean water tank (3).
 49. A method according to claim 48, wherein the distributor (25) is configured for preventing water to enter the second distributor outlet (30) during backwash when backwash water from the backwash bulb (7) is pressing the ball (26B) in the ball valve housing (26) against the ball seat (32), wherein the method comprises, compressing the backwash bulb and forcing backwash water in reverse through the first distributor outlet (20) and through the distributor (25) in reverse through the distributor inlet channel (29) while pressing the ball (26B) against the ball seat (32) by the pressure on the backwash water from the compression of the backwash bulb (7).
 50. A method according to claim 49, wherein a backwash tube (12, 12A) is provided which is connected to the upstream side for receiving contaminated backwash water from the upstream side of the filtration unit (5) and connected to a backwash receptacle (8) for dispensing the backwash water into the backwash receptacle (8) which is different from the dirt water container (2); wherein the method comprises during the compression of the backwash bulb (7), pressing the backwash water in reverse from the distributor inlet channel (29) to the membrane and in reverse through the membrane from the downstream side to the upstream side and further from the upstream side through the backwash tube (12, 12A) into the backwash receptacle (8).
 51. A method according to claim 46, wherein a one way check valve is provided between the dirt water container (2) and the upstream side of the filtration unit (5) and the method comprises closing the check valve by the pressure of the backwash water and preventing backwash water to be pressed into the dirt water container (2). 